An uninterruptible power supply, well known as a UPS, is typically used as a buffer between commercially supplied power and an electrical load, such as a computer, blood analyzer or other electronic equipment. If line voltage is interrupted, power to the load is maintained for a limited amount of time to operate the load during the interruption or to provide time to properly shut down the load without resulting damage. An on-line UPS typically comprises a converter, inverter, and battery charger. The UPS converts the commercially supplied AC power to DC power and then back to AC power. This conversion isolates the load equipment from spikes and sags in the commercially supplied power and corrects variances in line voltages. DC power is used to charge a battery. The battery can then be used to supply AC power to the load when the commercially supplied power is interrupted
In commercial applications, loads may change over time. As computer networks are expanded the load on the UPS increases. In order to meet this increase in demand, either a larger UPS is needed or a plurality of modular UPS units can be connected together to meet the required power level.
Known designs for a modular UPS have utilized one of two basic concepts. The first concept is to make each module an independent chassis. The modules can then be stacked or piled next to each other in order to make the necessary electrical connections. The problem with this concept is that it is difficult to move the unit and changing a module may require modules to be disconnected during the operation of the system. The second concept of designing a modular UPS has been to build a freestanding chassis that is essentially a large receptacle for the modules. This design solves the problems of mobility and service, but increases the size of the unit, makes the unit more difficult to manufacture, and limits field expandability. Thus, there is a need for a modular UPS unit that is easy to maintain, expandable and easy to manufacture.